One of the subjects Jonathan Savage (the FellRNR running guy) discusses at length is heat acclimation training, where you train specifically in hot conditions to either prepare yourself to race in hot conditions or to successfully race in less extreme, even more normal temperatures.
This is of course amusing to me as we in Las Vegas (and most of the United States, admittedly) are currently suffering through a bout of extreme heat. And in Vegas, we’re used to high heat, with summer days topping 100° Fahrenheit (38° Celsius), but the 110-120°F heat we have now is even above our typical pay grade.
Thus, those of us who run in Vegas get to practice heat acclimation training whether we want to or not!
Of course, Savage refers mainly to winter training for a spring marathon. In the winter temperatures fall below freezing in most parts of the country. If eventually you have to run a marathon in 60-80°F weather (15-25°C), you’re going to get hit hard by relatively warm conditions, even though you’d love to have those conditions in the middle of August. Your body will have acclimated to the other extreme of those cold conditions.
On top of that, Savage typically runs ultra-marathons in more extreme conditions like the hot and dry Badwater 135 race. So he’s not just dealing with a slightly warm marathon in London or Boston. He’s dealing with potentially 100°F heat with doubly dehydrating dry conditions. So even if it’s negative celsius or fahrenheit outside he needs to bundle up to prepare for running in 100°F weather.
Now, all that said, just because you or I have no intention of attempting such a race coming out of winter doesn’t mean that heat acclimation isn’t valuable.
Even with no races on the horizon, running in summer heat and the resulting heat acclimation (within healthy reason: Don’t go taking extended runs once the temperatures are over 100° without an abundance of cooling resources and support)… has one additional key benefit.